So I tested the slam valve on an unregged dropout changer. Very impressive valve, IMO. The valve body I use with my regged setup is too shallow to accept the slam valve base, so I'm going to have to figure something out with it. I've been planning on completely drilling it out anyways.

I actually had to shim the slam valve base in the dropout changer with one of the old valve springs y0da sent me. I think there is a ton of variation over the years when it comes to valve depth.

The first thing I noticed is that the valve has a very short travel, probably about half of what you'd see a normal Nelson valve open to. Despite that, I had no problem getting to full velocity using a standard silver CCI mainspring and Lapco fluted hammer.

I got 34 above 250, with an average of 299 FPS. I could probably do more with a slightly lower velocity, I was running in the 280s before. I think this is a pretty good start.

I have extrapolated the values from your graph: 300,307,303,292,299,297,291,303,270,290,282,296,30 8,304,296,315,297,302,298,308,312,315,301,317,309, 309,316,313,317,302,295,272,277,262,249,219,203,17 7

It is corect?

When is the muzzle velocity of the shoots converted in kinetic energy (Joules) - for better comparsion of markers with different velocity setting - the best know results for nelsons are imho:

Your result is surely very, very good. And from one point of view you are on the 3. place... but from other point of view... when you have not some other problem with the marker (bad paint to barrel match, some leaks or so) then the new valve looks not much impressive for me -you are only few shoots above my miserable New Hammer with common valve and only 4mm ID powertube and 1996XJ Phantom has the same efficiency like you.